gu.

Noun

gules (uncountable)

1. Red, e.g. on a coat of arms, typically represented in engraving by vertical parallel lines.
   • The official blazon of the arms of Perth is "Gules, a Holy Lambe passant regardant staff and cross argent, with the banner of St. Andrew proper, all within a double tressure counter-flowered of the second": […].1956 July, Col. H. C. B. Rogers, “Railway Heraldry”, in Railway Magazine, page 480

See all 2 meanings of gules